Pressure-sensitive composition containing an aminoxysilicon compound

ABSTRACT

The invention relates to a method of contacting two components to form a pressure-sensitive adhesive (PSA) construction, wherein the first component comprises a conventional PSA and an aminoxysilicon compound and a second component comprises the same PSA and an amidosilicon compound. The method provides improved adhesive bond strength over an unmodified PSA construction.

This is a divisional of copending application(s) Ser. No. 07/303,783filed on 1-30-89, now abandoned.

The present invention relates to crosslinkable pressure-sensitiveadhesives and an improved method for forming a pressure-sensitiveadhesive construction. More particularly, the present invention relatesto a method of contacting two distinct pressure-sensitive adhesivecomponents to form the construction, wherein an aminoxysilicon compoundis incorporated in the first component and an amidosilicon compound isincorporated in the second component.

BACKGROUND OF THE INVENTION

It is well known in the adhesives art that significant improvement inadhesion to various substrates can be obtained by incorporating variousadhesion promoters into adhesive compositions or employing such adhesionpromoters in primer compositions for coating the substrate. Developmentof a wideranging adhesives art has benefited from this method ofadhesion improvement and various organosilanes have been typicallyemployed as the adhesion promoter.

Organosilanes which are useful in these applications generally containhydrolyzable groups (e.g., halogen, alkoxy) attached to the silicon atomthereof which generate silanol groups upon contact with ambientmoisture, and thus readily form chemical and/or physical bonds withmineral and metal surfaces. Also attached to the silicon of theorganosilane adhesion promoter is an organic moiety which is reactivewith, or at least shows some affinity towards, one of the components ofthe adhesive (usually the polymer). This latter requirement usuallylimits the practical utility of a specific organosilane to particularadhesive-substrate combinations. In this way, a chemical or physical"molecular bridge" is believed to be formed between the adhesive and thesubstrate which results in the observed macroscopic improvement inadhesion.

Thus, for example, U.S. Pat. No. 3,644,245 to Flanagan et al. discloseshot melt adhesive compositions having improved adhesion under conditionsof high humidity. These compositions comprise a synthetic polymer baseand hydrolyzable silanes containing such organic groups as phenyl,vinyl, epoxy, mercapto, amino, ethyl, methyl and methacryloxypropyl.

Additionally, the adhesion to a substrate, as well as the cohesivestrength of an adhesive composition, may be augmented by at leastpartially cross-linking the adhesive. Various examples of this methodexist in the art, which method is illustrated by U.S. Pat. No. 3,657,379to Hilbelink et al. This disclosure teaches adhesive systems comprisingseparated reactive components wherein (1) a first reactive polymer ismixed with a curing agent for a second reactive polymer to yield onecomponent and (2) a second reactive polymer is mixed with a curing agentfor the first reactive polymer to form another component. When thereactive materials from the two components are mixed, the curing agentsreact with their respective reactive polymers to give strong adhesivebonds.

A distinct category of adhesives which comprises natural or syntheticrubbers and resin tackifiers is known in the art as "pressure-sensitiveadhesives" (PSAs). PSAs uniquely maintain a permanent "tack" whichprovides a bond of measurable strength immediately upon contact withanother surface. Again, adhesion to a substrate, as well as the cohesivestrength of the PSA composition itself, can be improved by curing thePSA.

A cured PSA based on a polyether having at least one silicon-containinghydrolyzable group in its molecule is disclosed by Hirose et al. in U.S.Pat. No. 4,463,115. This composition also contains a tackifier and,optionally, a silanol condensation catalyst for accelerating the curingreaction. It is stated that the resulting PSA has good adhesiveproperties and can be prepared substantially without the use of asolvent.

In a subsequent U.S. Pat. No. 4,665,127, Hirose et al. extended theabove concept to include a wide variety of polymers having at least onereactive silicon-containing group combined with an organic aluminum ororganic zirconium catalyst. These PSA compositions are said to haveexcellent heat resistance and releasability from substrates such as asilicone-coated release paper.

In U.S. Pat. No. 3,707,518, Bemmels et al. disclose a self cross-linkingpressure-sensitive acrylate adhesive and tape which comprises acopolymer that includes a small amount of an alkoxy silyl polymerizablecrosslinking monomer. Also included in these compositions is 2-6 partsby weight of an acid monomer which acts as a built-in catalyst andcauses the adhesive copolymer to cure at ordinary temperatures.

Aside from silicone-based PSAs, the use of silanes as adhesion promotersor compositions wherein reactive silicon groups are chemically attachedto organic molecules to promote cure therebetween, silicones aregenerally known in the art to be abhesive materials (i.e., they impartgood release of adhesives) and have, indeed, been widely employed inrelease liners for pressure-sensitive tape. Surprisingly, as disclosedin three copending applications (Ser. No. 181,763, filed on Apr. 14,1988, now U.S. Pat. No. 5,037,886; Ser. No. 189,004, filed on May 2,1988, now U.S. Pat. No. 4,831,080; and Ser. No. 216,609, filed on July8, 1988, now U.S. Pat. No. 4,906,695), Blizzard and Swihart discovered amethod for contacting two components to form a pressure-sensitiveadhesive (PSA) construction, wherein the first component comprises aconventional PSA and a reactive organopolysiloxane and the secondcomponent comprises the PSA and a cure agent for the organopolysiloxane.The method provides improved adhesion, which generally increases withthe passage of time, over the unmodified PSA.

SUMMARY OF THE INVENTION

It has now been further discovered that certain aminoxysilicon compoundsand amidosilanes may also be employed according to the methods describedby Blizzard and Swihart, cited supra. The present invention, therefore,relates to a method for forming a crosslinkable pressure-sensitiveadhesive construction comprising contacting a first component comprising

(I) a pressure-sensitive adhesive; and

(II) an aminoxysilicon compound having from 1 to 100 silicon atoms permolecule, from 3 to 10 aminoxy groups per molecule and at least oneradical selected from the group consisting of monovalent hydrocarbonradicals and halogenated monovalent hydrocarbon radicals per siliconatom, said aminoxy group having a general formula -OX, wherein X isselected from the group consisting of -NR₂ and a heterocyclic amine, Rbeing a monovalent hydrocarbon radical, with a second componentcomprising

(III) a further portion of said pressure-sensitive adhesive; and

(IV) an amidosilicon compound selected from the group consisting of

(a) a polymer consisting essentially of siloxane units selected from thegroup consisting of alkylmethylsiloxane units having 1 to 8 carbon atomsin the alkyl radical thereof and phenylmethylsiloxane units, saidpolymer having at least two amido groups of the formula ##STR1## in itsmolecule, wherein R'" represents an organic radical selected from thegroup consisting of methyl, ethyl and phenyl and Me denotes a methylradical, and

(b) an amidosilane having the general formula ##STR2## wherein R"" is anorganic radical selected from the group consisting of methyl, vinyl andphenyl and R'" and Me have been previously defined.

This invention further relates to compositions comprising thepressure-sensitive adhesive and the aminoxysilicon compound, and tocompositions comprising the pressure-sensitive adhesive and theamidosilicon compound, employed in the above described method.

DETAILED DESCRIPTION OF THE INVENTION

In the method of the present invention, a first component comprising (I)a pressure-sensitive adhesive (PSA) and (II) an aminoxysilicon compoundis contacted with a second component comprising (III) the samepressure-sensitive adhesive and (IV) an amidosilicon compound to form aPSA construction. While not wishing to be bound by any particularmechanism, it is believed that after the PSA construction is formed, theaminoxysilicon compound and the amidosilicon compound interact withatmospheric moisture to provide a "permanent set" to the adhesivesystem. Permanent set, as used herein, refers to the irreversibleincrease with time of the adhesive bond between the first and secondcomponents. This interaction can, of course, be hastened at elevatedtemperatures. The individual components, however, may generally bestored for prolonged periods under ambient conditions (e.g., roomtemperature and less than 50% relative humidity) as long as they are notin contact with each other.

As far as is known, the exact nature of the pressure-sensitive adhesive(I) employed in the method and composition of the present invention isnot critical to operability. The only limitation to this generaloperability is that the PSA have a reasonable degree of compatibilitywith the aminoxysilicon compound (II) and the amidosilicon compound(IV), each described infra. By compatibility it is meant that the PSAcomponents are not subject to phase separation upon standing and remainas homogeneous dispersions or solutions. Thus, it is believed that anyof the PSAs known in the art will function satisfactorily herein. ThesePSAs are based on a natural or synthetic rubber which has been mixedwith a tackifier resin and, optionally, with various fillers,plasticizers, extender oils, catalysts, preservatives, antioxidants,stabilizers, or other ingredient normally employed in the preparation ofPSAs. The PSAs suitable for use in the methods and compositions of thepresent invention may be based on natural rubber and/or one or moresynthetic rubber such as butyl, silicone, acrylic, styrene-butadiene,acrylonitrile-butadiene, polyisobutylene, isoprene, isopreneisobutylene,chloroprene, polyvinylether, chlorinated and polyurethane rubbers, andthe like. Typical resin tackifiers used in conjunction with theserubbers include rosin, hydrocarbon resins, terpene resin, siloxane resinand the like. Particularly preferred PSAs include those based onstyrene-butadiene and acrylic polymers.

The pressure-sensitive adhesives of ingredient (I) are well known in theart and further description thereof is considered unnecessary. Many ofthese materials are available commercially.

Ingredient (II) of the present invention is an aminoxysilicon compoundhaving from 1 to 100 silicon atoms per molecule in which there are from3 to 10 aminoxy groups per molecule and at least one monovalenthydrocarbon radical or halogenated monovalent hydrocarbon radical persilicon atom. The aminoxysilicon compound can be a silane or a siloxane.The aminoxy group which is bonded to the silicon atoms throughsilicon-oxygen bonds can be represented by the general formula -OXwherein X is a monovalent amine radical selected from the groupconsisting of -NR₂, in which R represents a monovalent hydrocarbonradical, and a heterocyclic amine. Specific examples of the -NR₂ groupsinclude N,N-diethylamino, N,N-ethylmethylamino, N,N-dimethylamino,N,N-diisopropylamino, N,N-dipropylamino, N,N-dibutylamino,N,N-dipentylamino. N,N-dihexylamino, N,N-dicyclohexylamin,N,N-methylpropylamino, N,N-methylbutylamino, N,N-diphenylamino,N,N-ditolylamino, N,N-methylphenylamino and N,N-methylnaphthylamino. Theheterocyclic amines can be illustrated by such groups as ethylenimino,pyrrolidino, piperidino and morpholino.

When the aminoxysilicon compound has one silicon atom, it may berepresented by the general formula R'Si(OX)₃, in which R' can be amonovalent hydrocarbon radical or halogenated monovalent hydrocarbonradical. R' can be illustrated by methyl, ethyl, phenyl, vinyl, hexyl,octadecyl, cyclohexyl, butyl, heptyl, octyl, benxyl, phenylethyl,naphthyl, propyl, isopropyl, chlorophenyl, 3,3,3-trifluoropropyl,beta-(perfluoropentyl) ethyl, iodonaphthyl, bromoheptyl, and the like.

The aminoxysilicon compounds which have more than one silicon atom permolecule can be linear polysiloxanes and cyclic polysiloxanes. They canbe homopolymers, copolymers or mixtures of the siloxanes as well asmixtures of the siloxanes and silanes. The silicon atoms of thesiloxanes are linked together through silicon-oxygen-silicon bonds, withthe remaining valences of the silicon atoms not bonded to aminoxy groupsbeing bonded to monovalent radicals as defined by R' above. Theseaminoxy siloxanes can be illustrated by the aminoxysilicon compoundsdescribed in U.S. Pat. No. 3,817,909 to Toporcer et al., assigned to theassignee of the present invention and hereby incorporated by reference.

It is preferred that the aminoxysilicon compound be selected fromcopolymers of polydimethylsiloxane having the general structure ##STR3##wherein Me hereinafter denotes a methyl radical and R" is independentlyselected from methyl or ethyl radicals. In the above formula, the valueof m may range from 1 to about 5,000, preferably from 1 to 100, while nmay be 2 to about 50, preferably from 2 to 10. A highly preferredaminoxysilicon compound has the average structure ##STR4## in which Ethereinafter denotes an ethyl radical.

The aminoxysilicon compounds of the present invention are known in theart and can be prepared by the method shown in U.S. Pat. No. 3,441,583.

Ingredient (III) of the present invention is a further portion of thesame PSA as ingredient (I).

The amidosilicon compound (IV) may be selected from homopolymers orcopolymers consisting essentially of alkylmethylsiloxane units orphenylmethylsiloxane units. The alkyl radical of the alkylmethylsiloxaneunits may contain from 1 to 8 carbon atoms, but it is preferred that thealkyl group is also a methyl radical. For the purposes of the presentinvention, at least two amido groups must be present on each polymer orcopolymer molecule. The amido groups may be attached to main-chainsilicon atoms or to terminal silicon atoms and has the general structure##STR5## in which R'" represents an organic radical selected from thegroup consisting of methyl, ethyl and phenyl. As discussed aboveingredient (IV) must form a compatible system when mixed with thepressure-sensitive adhesive (III). Therefore, the degree ofpolymerization of the polymer or copolymer containing amido groups maynot exceed a value consistent with this requirement. An example of sucha homopolymer is represented by the formula

    Me.sub.2 (A)SiO(Me.sub.2 SiO).sub.x Si(A)Me.sub.2

in which A denotes the group ##STR6## and x is of such a value that thepolymer is compatible with the particular PSA under consideration.

Alternatively, it is preferred that the amidosilicon compound isselected from amidosilanes having the general formula ##STR7## whereinR"" represents an organic radical selected from the group consisting ofmethyl, vinyl and phenyl and R'" has its previous definition. Thesilanes include, for example, methyvinyldi-(N-methylacetamido) silane,dimethyldi-(N-methylacetamido) silane,methylphenyldi-(N-methylacetamido) silane,methylvinyldi-(N-ethylacetamido) silane, dimethyldi-(N-ethylacetamido)silane, methylphenyldi-(N-ethylacetamido) silane,methylvinyldi-(N-phenylacetamido) silane, dimethyldi-(N-phenylacetamido)silane, and methylphenyldi(N-phenylacetamido) silane. A preferredamidosilicon compound of the present invention ismethylvinyldi-(N-methylacetamido) silane.

The amidosilanes are well known in the art and can be prepared byreacting a cholorosilane with an alkali metal salt of an appropriateN-organoacetamide. The polymers containing the amido groups may, inturn, be prepared from the amidosilane by reacting an excess of thiscompound with a silanol-functional siloxane polymer, the polymer beingadded to the amidosilane to produce the product.

Although the above described aminoxysilicon compounds and amidosilanesmay generally be employed in the method of the present invention, it hasbeen found that certain PSAs are themselves incompatible with some ofthese compounds. The skilled artisan will readily determine which ofthese compounds are compatible with a given PSA.

The compositions of this invention can further comprise typicaladjuvants employed in the preparation of pressure sensitive adhesives,such as catalysts, fillers, pigments, dyes, fungicides, bacteriocides,stabilizers, antioxidants and cure-control additives, if desired.

In order to practice the present invention, the first component of thisinvention is prepared by thoroughly mixing the aminoxysilicon compound(II) with the PSA (I) such that the aminoxysilicon compound constitutesfrom about 1 to 20 percent of the total weight of (I) plus (II), on asolids basis. Preferably, the aminoxysilicon compound constitutes from 1to 10 percent by weight of (I) plus (II).

In a similar manner, the second component of this invention is preparedby thoroughly mixing a curing amount of the amidosilicon compound (IV)with the PSA (III). By "curing amount" it is meant at least an amountsufficient to improve the adhesion between the two components asdemonstrated by an increase in bond strength and/or increased cohesivefailure versus the unmodified PSA. Thus, the amount of amidosiliconcompound employed will vary according to the nature of the PSA, amountof the aminoxysilicon compound incorporated therein and the particularamidosilicon compound selected. Typically, this will vary from about 0.1to about 10 percent by weight of the amidosilane based on the totalweight of the amidosilicon compound (IV) plus the PSA (III), on a solidsbasis.

The compositions of the present invention, in which the aminoxysiliconcompound (II) is incorporated in a PSA (I), and in which theamidosilicon compound (IV) is incorporated in a PSA (III), are thusemployed as intermediates in the method of the present invention.

Those skilled in the art will readily arrive at optimum formulations byroutine experimentation. For example, when the PSA is selected from thepreferred systems based on acrylic or styrene-butadiene rubber, fromabout 1 to 10 percent by weight of the preferred aminoxysilicon compoundof formula (ii), above, are effectively employed in the first PSAcomponent and from about 0.1 to 10 percent by weight ofmethylvinyldi-(N-methylacetamido) silane are employed in the second PSAcomponent. As mentioned above, however, the maximum aminoxysiliconcompound content and amidosilicon compound content in the two componentsis limited by compatibility considerations and these ingredients mustnot separate from the PSA matrix to form their own macroscopic phases.It is, of course, recognized that separate phases may exist at amicroscopic level.

As will be readily recognized by those skilled in the art, the PSAs ofthe present invention may be supplied as a solution or dispersion in aninert organic solvent. By inert it is meant that the solvent does notreact with any of the other ingredients of the present invention. Theparticular solvent selected will generally depend upon the PSA employed.Thus, for a non-polar PSA such as a silicone or a butyl rubber, anon-polar solvent such as toluene, hexane, cyclohexane, mineral spiritsor xylene would be appropriate. For a polar PSA such as a urethane oracrylonitrile, a polar solvent such as acetone, ethyl acetate,tetrahydrofuran or dimethylformamide might be used. In general, the PSAscontemplated in the present invention are prepared and marketed in suchsolvent form and are well known in the art.

Any conventional mixing method may be used to mix the ingredients of theabove described components. For example, when the PSA is supplied insolution, relatively low shear mixers such as low speed blade mixers orPfaudlers may be used. When an all-solids PSA is to be used according tothe methods of the present invention, a high intensity mixer, such as aBanbury or roll mill, should be used to insure good dispersion of theingredients. As far as is known, the order of mixing is not critical tothe operability of this invention as long as the aminoxysilicon compoundand the amidosilicon compound are thoroughly dispersed in the respectivePSA.

After the above described first and second components are prepared, saidcomponents are contacted in the method of this invention to form apressure-sensitive adhesive construction. Ordinarily, each component iscoated onto a substrate before the contacting step is executed. Thus,this well known method in the art can be practiced using the componentsdisclosed herein by first coating a backer, such as a plastic ormetallic film or tape, with the first component of this invention andcontacting the resulting composite with the surface of a solidsubstrate, such as a metal or plastic, which was previously coated withthe second component of the present invention. It is also contemplatedthat a free film of the first and second components of the presentinvention may be prepared by coating each component onto a release lineras is commonly practiced in the art in certain bonding operations.

To form such coatings on substrates, solvent-based compositions of thisinvention can be diluted with a sufficient quantity of a good solventfor the respective components in order to provide a desired coatingconsistency. As described above, such solvents as hexane, heptane,toluene, xylene, mineral spirits or ketones are suitable for thispurpose, the exact choice being based on the nature of the PSAsinvolved, as is commonly practiced in the art. Coatings of suchsolvent-based first and second components may be applied to substratesby any of the methods commonly practiced in the coating arts. Forexample, they may be dipped, brushed, flow coated, blade coated orgravure coated onto a substrate. After coating the backer or solidsubstrate with the PSA composition, solvent is generally removed byevaporation at ambient temperature or by heating, as commonly practicedin the art. Alternatively, 100% solids coatings are also contemplatedherein. These may be applied to a substrate by, e.g., a calendaringoperation or one of the above mentioned techniques if the viscosity islow enough.

Those skilled in the art will recognize that both the aminoxysiliconcompound (II) as well as the amidosilicon compound (IV) react withwater. It is therefore preferred to store the PSA components containingthese ingredients in a dry (e.g., hermetically sealed) condition tillthey are to be contacted by the method of the present invention.

The constructions of the present invention may be used in many of theapplications currently being served by the PSAs described above (i.e.,ingredient I of the present invention). With the constructions of thepresent invention, however, the adhesion is improved and, with thepassage of time, the adhesive bond formed between the first and secondcomponents will generally increase in strength. This permanent setaspect of the present invention is, of course, an advantage in manyapplications wherein a strong bond, rather than reversibility thereof,is of primary importance. Such applications include bonding ofautomotive and decorative trim, permanent fastening devices such aspicture hooks, contact paper and labels, electronic component assembly,substrate lamination (e.g., metals, paper, plastic, floor tiles,carpeting), and the like.

EXAMPLES

The following examples are presented to further illustrate thecompositions and methods of this invention, but are not to be construedas limiting the invention, which is delineated in the appended claims.All parts and percentages in the examples are on a weight basis and allare reported on a solids basis unless indicated to the contrary.

The following materials were used to prepare the constructions of thepresent invention as well as comparative constructions:

CROSSLINKER A is an aminoxy-functional silicone consisting essentiallyof an N,N-diethylaminoxypolysiloxane having the formula ##STR8## whereinMe and Et hereinafter denote methyl and ethyl radicals, respectively.

SILANE B is a silane consisting essentially ofmethylvinyldi-N-methylacetamidosilane having the formula ##STR9##

MTO is a methyl trioximosilane having the structure ##STR10##

PDMS is a hydroxyl endblocked polydimethylsiloxane fluid having aviscosity of about 40 cS at 25° C.

DBTDA is dibutyltin diacetate.

EXAMPLES 1-2

An acrylic pressure-sensitive adhesive (PSA) solution, 76 RES 9105, wasmodified to form the constructions of the present invention. 76 RES 9105(Unocal Chemicals Division, Schamburg, Ill.) is described as a highperformance "self-crosslinking" pressure sensitive adhesive which is a45% solids solution of an acrylic resin polymer in an oxygenatedhydrocarbon solvent blend. A first component was prepared by thoroughlymixing the indicated amount of CROSSLINKER A with this PSA (see Table1). A second component was prepared by thoroughly mixing SILANE B withanother portion of the PSA solution, also indicated in Table 1. Each ofthese components was then applied to 5 mil aluminum foil, dried to forma 2 mil-thick film thereon and the coated foil was cut into 1 inch-widestrips. The foil strips bearing the first and second PSA adhesive filmswere pressed together using a 10 pound steel roller at room temperatureto form a lap joint having a 1/2 inch overlap (i.e., a total of 1/2square inch contact surface). The same procedure was followed in thepreparation of (Comparative) Example 1, which served as a control andcontained no additives in either PSA layer. The lap joints were aged atroom temperature for various periods and then tested (at roomtemperature using a pull rate of 1/2 inch/minute) to determine shearadhesive strength. Results are presented in Table 1, wherein the shearstrength is reported in pounds per square inch (psi).

                  TABLE 1                                                         ______________________________________                                                        (Comparative)                                                                 Example 1 Ex. 2                                               ______________________________________                                        % CROSSLINKER A in                                                                              --            5.7                                           first component                                                               (solids basis)                                                                % SILANE B in     --            3.2                                           second component                                                              (solids basis)                                                                Shear                                                                         Adhesion (psi)                                                                After:                                                                         1 hour           66          59                                               1 day            60          86                                               2 days           63          73                                               7 days           64           84*                                            28 days           69          93                                              ______________________________________                                         *Aluminum foil tore; actual shear strength greater than indicated.       

EXAMPLES 3-4

A styrene-butadiene rubber based PSA solution, DURO-TAK 36-6045, wasmodified and tested according to the procedures of Example 2, as shownin Table 2. DURO-TAK 36-6045 (National Starch and Chemical Corp.,Bridgewater, N.J.) is described as a 48% solids solution in toluene,heptane and isopropyl alcohol having a viscosity of about 5,500 cP at25° C. Again, a control construction (Comparative Example 3) wasprepared to illustrate the unmodified styrene-butadiene PSA. Shearadhesion results are shown in Table 2, wherein a one inch overlap wasused in the case of the control construction.

                  TABLE 2                                                         ______________________________________                                                        (Comparative)                                                                 Example 3 Example 4                                           ______________________________________                                        % CROSSLINKER A in                                                                              --            5.7                                           first component                                                               (solids basis)                                                                % SILANE B in     --            3.2                                           second component                                                              (solids basis)                                                                Shear                                                                         Adhesion (psi)                                                                After:                                                                         1 hour           7            98*                                             1 day            10           87*                                             2 days           11           93*                                             7 days           9            89*                                            28 days           9            89*                                            ______________________________________                                         *Aluminum foil tore; actual shear strength greater than indicated.       

EXAMPLES 5-9

The 76 RES 9105 acrylic pressure-sensitive adhesive solution, describedabove, was modified to form the PSA constructions shown in Table 3.These constructions were tested as described in Examples 1-2 with theexception that 5 mil thick stainless steel foil was use instead of thealuminum foil.

                  TABLE 3                                                         ______________________________________                                                    (Comparative)                                                                 Ex. 5 Ex. 6  Ex. 7   Ex. 8 Ex. 9                                  ______________________________________                                        % CROSSLINKER A                                                                             20      20     10       1.0                                                                                 1.0                               first component                                                               (solids basis)                                                                % SILANE B      0.1   10       1.0  10      0.1                               second component                                                              (solids basis)                                                                Shear                                                                         Adhesion (psi)                                                                After:                                                                         1 hour       24      63     38    181   141                                   1 day        36      101    55    239   148                                   2 days       43      84     48    107   132                                   7 days       59      113    94    156   117                                  28 days       57      92     115   112   136                                  ______________________________________                                    

(Comparative) Example 5 in Table 3 illustrates the reduced adhesivestrength obtained when there was an improper balance between CROSSLINKERA and SILANE B for this particular acrylic PSA.

EXAMPLE 10

The above described DURO-TAK 36-6045 styrene-butadiene rubber PSA wasmodified as shown in Table 4, wherein shear adhesion test results usingthe 5 mil thick stainless steel foil as the substrate are also reported.

                  TABLE 4                                                         ______________________________________                                                         Example 10                                                   ______________________________________                                        % CROSSLINKER A in    6.7                                                     first component                                                               (solids basis)                                                                % SILANE B in         4.2                                                     second component                                                              (solids basis)                                                                Shear                                                                         Adhesion (psi)                                                                After:                                                                         1 hour             76                                                         1 day             164                                                         2 days            194                                                         7 days            125                                                        28 days            --                                                         ______________________________________                                    

It is seen from the above Tables that the PSA constructions of thepresent invention provide improved shear adhesive strength versusunmodified acrylic and styrene-butadiene systems.

(COMPARATIVE) EXAMPLE 11

A first component of the DURO-TAK 36-6045 styrene-butadiene rubber PSAwas modified with 5.0 percent of MTO and a second component of this PSAwas modified with a mixture of 9.0 percent of polydimethylsiloxane and1.0 percent of DBTDA according to the above procedures. Shear adhesiontesting results, using the 5 mil thick aluminum foil as the substrate,are presented in Table 5.

                  TABLE 5                                                         ______________________________________                                               Shear                                                                         Adhesion (psi)                                                         ______________________________________                                               After:                                                                         1 hour   17                                                                   1 day    18                                                                   2 days   20                                                                   7 days   22                                                                  28 days   17                                                           ______________________________________                                    

It is known in the silicone sealants art that compositions containingthe above ingredients (i.e., the MTO, PDMS and DBTDA) would cure at roomtemperature. Nevertheless, the modification of the above PSA with thesematerials did not improve the shear strength as much as did themodifications according to the present invention.

Similar attempts to modify an acrylic PSA, with MTO in the firstcomponent and the PDMS and DBTDA in the second component, were alsoineffective.

EXAMPLE 12

The above described styrene-butadiene rubber PSA was modified byincorporating 6.7% of CROSSLINKER A in the first component and 4.2% ofSILANE B in the second component, as described in Example 10. Themodified PSA components were coated onto 5 mil thick stainless steelfoil. The effect of relative humidity on adhesion performance wasevaluated by exposing the coated steel foils to (a) 100% relativehumidity (R.H.) at 60° C.: (b) essentially 0% R.H. at room temperature;and (c) ambient conditions. After storage for the times indicated inTable 6, the components were pressed together for one hour and sheartested using a one inch overlap.

                  TABLE 6                                                         ______________________________________                                        Storage Condition                                                                          Storage Time                                                                             Shear Strength (psi)                                  ______________________________________                                        100% R.H.    1      day     154                                               "            7      days    147                                               "            14     days    105                                               "            28     days    115                                                0% R.H.     1      day     252                                               "            7      days    231                                               "            14     days    264                                               "            28     days    281                                               Ambient      1      hour     76                                               ______________________________________                                    

It is seen from Table 6 that exposure of the coated PSA foils of thepresent invention to high humidity reduces ultimate shear adhesion, butthe bond strength is still quite high. Furthermore, the coated foilsretained their tack after storage at the high humidity.

We claim:
 1. A composition consisting essentially of:(I) apressure-sensitive adhesive selected from those based on acrylic,styrene-butadiene, acrylonitrile-butadiene, polyisobutylene, isoprene,isoprene-isobutylene, chloroprene, polyvinylether, chlorinated orpolyurethane rubber; and (II) an aminoxysilicon compound having thestructure ##STR11## wherein Me denotes a methyl radical, R" isindependently selected from the group consisting of methyl and ethylradicals, m is 1 to about 5,000 and n is 2 to about 50, saidaminoxysilicon compound constituting from about 1 to 20 percent of thetotal weight of said ingredients (I) and (II).
 2. The composition ofclaim 1, wherein m of said aminoxysilicon compound is 1 to 100 and n ofsaid aminoxysilicon compound is 2 to
 10. 3. The composition of claim 2,wherein said pressure-sensitive adhesive is based on a rubber selectedfrom the group consisting of acrylic and styrene-butadiene polymers. 4.The composition of claim 3, wherein said aminoxysilicon compound (II)has the structure ##STR12## in which Me and Et denote a methyl and anethyl radical, respectively.